The House of Representatives could vote as early as Friday on a landmark energy and global warming bill. And as a federal report made clear again last week, a strong bill to combat the worst impacts of climate change won't come a moment too soon.

The report, prepared by the United States Global Change Research Program, a group of 13 federal agencies and the White House, is both ominous and guardedly optimistic. It says some effects of climate change -- like higher temperatures and changes in agriculture -- are already being felt in the United States. Others, like the loss of coastal land and the extinction of some species, likely cannot be avoided. But even more disastrous future impacts can be mitigated if the nation -- and the world -- act now.

The international scientific community has concluded that global warming is caused largely by the emission of carbon dioxide and other heat-trapping "greenhouse" gases. The House bill -- the American Clean Energy and Security Act of 2009 -- would place a cap on carbon emissions and establish a mechanism for auctioning off emission allowances to power plants and industries. Those companies would be free to sell or trade the allowances among themselves, as long as the overall cap was not surpassed.

The cap would tighten over a period of years. The bill orders a 17 percent cut in greenhouse gas emissions below 2005 levels by 2020 and an 83 percent cut by 2050. So companies would have a powerful financial incentive to find new and greener ways to operate.

The Congressional Budget Office concluded that the bill would actually trim the federal budget deficit over the next decade because of the billions of dollars that it would bring in through the sale of emission allowances.

But it could be far stronger. Under President Barack Obama's original proposal, all the emission allowances would be purchased at auction, with some of the proceeds going to pay for tax cuts, help energy consumers pay for higher bills and jump-start clean energy technologies. But heavy lobbying has chipped away at that plan. The bill now gives away more than three-quarters of the emission allowances during the program's opening years. By 2031, about 70 percent of the allowances would have to be purchased.

That's a mistake. Although energy companies would be required to help consumers with rising energy costs, it makes more sense for the government to sell the allowances and provide relief directly to consumers.

There are plenty of other imperfections in the bill, born of compromises with farm interests, coal producers and others. Although there is urgency in passing climate change legislation this year, there is still time for improvement.

President Obama should turn his focus to this historic legislation to make sure it is as fair as it can be to ordinary Americans without compromising the need to cut greenhouse gases. Such action would give the United States the moral authority to push for other nations to do their part to confront this grave environmental threat.